So I did this post yesterday on Iconix and how they put little images in the email "from:" field, and a few other blogs (this one, for example) linked to it. All these blogs mentioned something called X-Face, but since they are written in German, I wasn't sure what they were talking about. It turns out that at the end of last century, there was a standard that allowed embedding a small 48x48px bitmap pic into the email headers so that people could match addresses (or IPs) with faces. You can learn everything about X-Face in this Wiki entry and generate your own little pixelated you right here.